Method of producing an organic light-emissive device

ABSTRACT

A method of producing an organic light-emitting device comprising a patterned electroluminescent polymer layer arranged between two electrodes such that charge carriers can move between the first and second electrodes an the electroluminescent polymer layer, the method comprising the steps of (a) providing a substrate comprising the first electrode, (b) depositing solid particles comprising the electroluminescent polymer onto selected portions of the surface of the substrate, and (c) securing to the substrate those solid particles comprising electroluminescent polymer particles deposited onto the substrate in step (b) to form the patterned electroluminescent polymer; and (d) forming the second electrode over the surface of the electroluminescent

[0001] The present invention relates to a method of producing an organiclight-emissive device comprising an electroluminescent polymer.

[0002] Organic light-emitting devices typically comprise a layer of anelectroluminescent polymer arranged between an anode and a cathode suchthat positive and negative charge carriers can move between the anodeand cathode and the electroluminescent polymer layer.

[0003] Conventionally, the electroluminescent polymer layer is depositedby coating a substrate comprising the anode or cathode with a solutionof the electroluminescent polymer or a solution of a precursor to theelectroluminescent polymer layer followed by conversion of the precursorto the electroluminescent polymer. Coating of the substrate with suchsolutions is, for example, typically carried out using a spin-coating orblade-coating technique.

[0004] In the case that a patterned light-emissive layer is required,ink-jet printing has been used to selectively deposit a solution of theelectroluminescent polymer or its precursor on selected portions of thesubstrate.

[0005] According to a first aspect of the present invention, there isprovided a method of producing an organic light-emitting devicecomprising a patterned electroluminescent polymer layer arranged betweentwo electrodes such that charge carriers can move between the first andsecond electrodes and the electroluminescent polymer layer, the methodcomprising the steps of (a) providing a substrate comprising the firstelectrode, (b) depositing solid particles comprising theelectroluminescent polymer onto selected portions of the surface of thesubstrate, (c) securing to the substrate those solid particlescomprising electroluminescent polymer particles deposited onto thesubstrate in step (b) to form the patterned electroluminescent polymerlayer; and (d) forming the second electrode over the surface of theelectroluminescent polymer layer opposite the first electrode.

[0006] The steps of depositing the solid particles comprisingelectroluminescent polymer onto selected portions of the surface of thesubstrate, and securing them to the substrate may be carried out by anelectrostatic technique of the type used in electrostatic printing.Reference is made to “Electromagnetics” by John D. Kraus, McGraw-HillPublishing Co. 1999 and “Electromagnetics: with Applications” by John D.Kraus, McGraw-Hill Publishing Co. 1999.

[0007] The patterned layer of electroluminescent polymer may for exampleconsist of a two-dimensional array of pixels of one or moreelectroluminescent polymers.

[0008] The method preferably further comprises a step of selectivelycovering those portions of the substrate onto which theelectroluminescent polymer was not deposited with an insulator materialto form an insulating matrix around the pixels of electroluminescentpolymer, wherein the insulator material is preferably also deposited assolid particles of said insulator material, which are then secured tothe substrate.

[0009] The solid particles comprising the electroluminescent polymerpreferably have a particle size of about 100 nm. The insulator materialis preferably black.

[0010] According to a preferred embodiment of the present invention,there is provided a method of producing an organic light-emitting devicecomprising a patterned electroluminescent polymer layer arranged betweentwo electrodes such that charge carriers can move between the first andsecond electrodes and the electroluminescent polymer layer, the methodcomprising the steps of (a) providing a substrate comprising the firstelectrode, (b) providing solid particles comprising theelectroluminescent polymer and capable of supporting an electrostaticcharge of a first polarity; (c) providing a transfer surface havingportions which are independently capable of supporting an electrostaticcharge and applying an electrostatic charge of a second polarity toselected portions of the transfer surface; (d) selectively transferringsaid solid particles comprising electroluminescent polymer to saidcharged selected portions of said transfer surface by virtue of anelectrostatic interaction between said selected portions of the transfersurface and the solid particles; and (e) contacting the transfer surfacewith the substrate so as to transfer the solid particles held thereon toselected portions of the substrate and securing them to the substrate tothereby form a patterned electroluminescent polymer layer on thesubstrate; and (f) forming the second electrode over the surface of thepatterned electroluminescent polymer layer opposite the first electrode.

[0011] The electrodes are preferably adapted such that selected portionsof the patterned electroluminescent polymer layer can be independentlyactivated.

[0012] In one embodiment, the second electrode is formed by applying apre-patterned second electrode to the surface of the patternedelectroluminescent polymer layer.

[0013] An embodiment of the present invention shall now be described, byway of example only, with reference to the accompanying drawings, inwhich:

[0014]FIG. 1 shows a schematic cross-sectional view of a light-emittingdevice produced according to a method of the present invention;

[0015]FIG. 2 shows schematically the formation of a light-emissive layeraccording to a method of the present invention; and

[0016]FIG. 3 shows a schematic plan view of a section of a device at anintermediate stage in its production by a method according to anembodiment of the present invention.

[0017] With reference to FIGS. 1 and 2, a glass base 1 is pre-coatedwith a layer of indium tin oxide 2 to provide an anode substrate 5. Theapparatus shown in FIG. 2 is used to deposit a light-emissive layer 3 onthe surface of the anode substrate 5 in a batch process. According toone variation, a flexible substrate base is used instead of the rigidglass base, which allows the method described below to be carried out aspart of a continuous roll-to roll manufacturing process. The ITO anodelayer may be patterned depending on how the final device is to beoperated. For example, an anode patterned as a plurality of rows may beused in conjunction with a cathode patterned as a plurality of columnsto provide the possibility for independently addressing selectedportions of the light-emissive layer.

[0018] In FIG. 2, hopper 10 contains a supply of solid particles 12 madefrom an electroluminescent polymer. The electroluminescent polymer may,for example, be a polyphenylene vinylene or a polyfluorene, or one ofthe other known electroluminescent polymers mentioned in the review ofelectroluminescent polymers in Adv. Mater. 2000, 12, no.23, 1737-1750.

[0019] The solid particles are fed from the hopper by means of stirrer14 and supply roller 16 towards a charging roller 18, which is providedwith an insulating surface coating that does not dissipate electrostaticcharge. A thin layer of charged solid particles is formed on thecharging roller by means of the blade 20, which is made from stainlesssteel, and the insulating surface of the charging roller 18. The surfaceof developing roller 18 is adapted such that an electrostatic charge ofa polarity reverse to that of the electrostatic charge of the solidparticles on the charging roller can be applied to selected portionsthereof by means of a laser (not shown) to create an electrostatic imageon the surface of the developing roller 22. With rotation of thedeveloping roller 18 and the charging roller 16, solid particles of theelectroluminescent polymer are transferred from the charging roller tothose portions of the surface of the developing roller to which anelectrostatic charge or reverse polarity has been applied by virtue ofan electrostatic interaction between the charge on the solid particlesand on the selected portions of the surface of the developing roller. Animage of solid polymer particles is thus developed on the surface of thedeveloping roller 22.

[0020] The solid particles of electroluminescent polymer that have beentransferred to the developing roller 22 are then transferred on to thesurface of the anode substrate 5 and fused to the surface of the anodesubstrate 5 by means of fusing rollers 24. In this way, a patternedlayer of electroluminescent polymer can be provided on the surface ofthe anode substrate 5. Alternatively, a solvent vapour, spray orsaturated solvent atmosphere may be used to homogenise the polymerparticles into a polymer film (vapour fusion) instead of using fusingrollers.

[0021] The solid particles of electroluminescent polymer preferably havea particle size of about 100 nm. A supply of such particles can beproduced, for example, according to the following methods.

[0022] A solution of the electroluminescent polymer in a suitablesolvent is sprayed using an airbrush into a swirling beaker of a liquidin which the electroluminescent polymer is not soluble. This results inthe precipitation of particles of the electroluminescent polymer, whichcan be isolated by filtration followed by drying. The size of theparticles is determined by the nozzle size of the airbrush, the pressureat which the solution of the electroluminescent polymer is sprayedthrough the nozzle of the airbrush and the concentration of the solutionof the electroluminescent polymer. In the case of polyfluorenes, tolueneis one example of a suitable solvent; others are described in, forexample, WO00/59267. Examples of suitable solvents for solublepolyphenylene vinylenes include dichloromethane and chloroform.

[0023] Alternatively, the solid particles of electroluminescent polymercan be prepared according to a micella technique by forming an emulsionin water in an ultrasonic bath. Formation of micelles is described in,for example, “Micelles, Microemulsions and Monolayers” by Dinesh O Shah(Editor), Marcel Dekker 1998.

[0024] In some light-emitting devices, a 2D array of pixels ofelectroluminescent polymer is required. In such a case, it is preferablethat each pixel 32 be electrically insulated from surrounding pixels 32by providing a 2D matrix of insulator material 30 around the pixels, asshown in FIG. 3. This matrix of insulator material can be provided afterforming the pixels using the same method used to form the pixels asdescribed above except that solid particles of the insulator materialare used instead of the solid particles of electroluminescent polymer.The insulator material may, for example, be a powder comprising aplastic and a pigment as commonly used as a laser printer toner.

[0025] The insulator material is preferably black in order to improvethe contrast of the device.

[0026] In some cases, it is desired to form pixels of differentelectroluminescent polymers in order to produce a device that can beused to emit light of more than one colour. Such an array of pixels ofdifferent electroluminescent polymers can be produced by the serialdeposition of solid particles of each electroluminescent polymeraccording to the electrostatic technique described above.

[0027] For example, the anode substrate could be passed successivelythrough a blue station, a red station, a green station and an insulatingstation for respectively forming on the surface of the anode substratepixels of polymers which are capable of emitting blue, red and greenlight, respectively, and then forming a matrix of insulating materialaround the electroluminescent polymer pixels.

[0028] A suitably patterned cathode 4 may be deposited on the layer orpixels of electroluminescent polymer by any conventional technique suchas vacuum evaporation. In some instances, the fusing process may resultin an uneven layer or uneven pixels of electroluminescent polymer. Insuch an instance, it is preferable to apply a pre-patterned cathode tothe side of the electroluminescent polymer layer or pixels opposite theanode substrate. Such a pre-patterned cathode also serves to effectivelyencapsulate the electroluminescent polymer layer or pixels. According toone variation, the cathode strips or sheet may be put in place beforethe fusing process.

[0029] The light-emitting device may also have additional layers such asa hole transport polymer layer between the anode and theelectroluminescent polymer layer and/or an electron transport polymerlayer between the cathode and the electroluminescent polymer layer. Suchlayers may also be formed by the deposition of solid particlescontaining the respective polymer according to the technique describedabove.

[0030] The anode substrate 5 is preferably flexible so that it can, becurved during the process of applying the patterned electroluminescentlayer thereto.

1. A method of producing an organic light-emitting device comprising a patterned electroluminescent polymer layer arranged between two electrodes such that charge carriers can move between the first and second electrodes and the electroluminescent polymer layer, the method comprising the steps of (a) providing a substrate comprising the first electrode, (b) depositing solid particles comprising the electroluminescent polymer onto selected portions of the surface of the substrate, and (c) securing to the substrate those solid particles comprising electroluminescent polymer particles deposited onto the substrate in step (b) to form the patterned electroluminescent polymer layer; and (d) forming the second electrode over the surface of the electroluminescent polymer layer opposite the first electrode.
 2. A method according to claim 1 further comprising the step of selectively covering those portions of the substrate onto which the electroluminescent polymer was not formed with an insulator material.
 3. A method according to claim 2 comprising depositing solid particles of said insulator material to said substrate and securing the solid particles of insulator material to the substrate.
 4. A method according to claim 3 wherein the electroluminescent polymer particles have a particle size of about 100 nm.
 5. A method according to claim 2 wherein the insulator material is black.
 6. A method of producing an organic light-emitting device comprising a patterned electroluminescent polymer layer arranged between two electrodes such that charge carriers can move between the first and second electrodes and the electroluminescent polymer layer, the method comprising the steps of (a) providing a substrate comprising the first electrode, (b) providing solid particles comprising the electroluminescent polymer and capable of supporting an electrostatic charge; (c) providing a transfer surface having portions which are independently capable of supporting an electrostatic charge and applying an electrostatic charge to selected portions of the transfer surface; (d) applying said solid particles comprising electroluminescent polymer to said charged selected portions of said transfer surface by virtue of an electrostatic interaction between said selected portions of the transfer surface and the solid particles; and (e) contacting the transfer surface with the substrate so as to transfer the solid particles held thereon to selected portions of the substrate and securing them to the substrate to thereby form a patterned electroluminescent polymer layer on the substrate; and (f) forming the second electrode over the surface of the patterned electroluminescent polymer layer opposite the first electrode.
 7. A method according to any preceding claim wherein the electrodes are adapted such that selected portions of the patterned electroluminescent polymer layer can be independently activated.
 8. A method according to any preceding claim comprising the step of applying a pre-patterned second electrode to the surface of the patterned electroluminescent polymer layer.
 9. A method according to any preceding claim wherein the substrate is a flexible substrate. 